1/2 inch tap (for threading stripped threads, duh)

Does any one know of a tap that can be used to repair stripped 1/2 inch threads. Many of times I come to home owner systems were they have stripped the threads in the ground and I (and the homeowner) don't want to replace the fitting due to it being in a bad spot (right by a wall) So I was wondering if there was a product like a riser extractor type product used for rethreading.

PVC? Galvanized? Poly? I think there is a tool you can use, but if it's poly or PVC just rip it out and do it over. I know it may take more time and especially if in a tight area but in the long run it will probably be better. I have done the soft marlex ell trick as well.